Grosvenor Britain & Ireland (‘Grosvenor’) has successfully transformed a Grade II Listed Hotel into three of the most sustainable, energy efficient apartments for rent in the UK. 119 Ebury Street has now become the first Listed building to receive a BREEAM ‘Outstanding’ rating in the UK for its proposed design. Grosvenor sought to create highly sustainable apartments which feature whole house ventilation and heat recovery; this was accomplished using the most recent engineering systems and low carbon technologies. One important aspect of the building that was hampering the ability to recover heat and create whole house ventilation was the original single glazed sash windows, which provided poor insulation. A total of 18 Series 25s were installed, which are a vertical sliding system with high capacity spring balances, ideal for treating larger windows that require thicker glass. The units were glazed with Pilkington Spacia, which is an evacuated sealed unit only 6mm thick with a centre pane U-value of 1.0. The secondary glazing treatment dramatically improved the overall U-value and assisted in achieving high airtightness levels.